Sheep preference for different tanniniferous tree fodders and its relationship with in vitro gas production and digestibility

Chemical composition, in vitro apparent dry matter digestibility (IVDMD), in vitro gas production (IVGP), preference, eating rate (ER) and selectivity of leaves from four forage trees were evaluated in hair sheep. In Experiment 1, fresh foliage of tanniniferous trees (Lysiloma latisiliquum, Acacia pennatula and Piscidia piscipula) and Brosimum alicastrum were offered ad libitum to hair sheep for 4 h in a cafeteria experiment. Effective eating time and ER (g/dry matter (DM)/min) were estimated from instantaneous measurements taken every minute during the first and fourth hour. In Experiment 2, B. alicastrum was withdrawn and preference for the tanniniferous tree fodders was determined. Foliage samples were collected daily for chemical composition. In vitro gas production profiles for each fodder tree were determined at 3, 6, 9, 12, 15, 18, 21 and 24 h of incubation, with IVDMD measured at the 24th hour. During each experiment, selectivity was calculated for each animal on a daily basis. L. latisiliquum had the highest content of condensed tannins (CT) and A. pennatula the highest content of total polyphenols (TP) and total tannins (TT). Differences in IVGP with and without polyethylene glycol (PEG) indicated that the polyphenolic compounds of A. pennatula had the highest biological activity (P<0.001). The highest IVDMD was obtained with B. alicastrum (P<0.001). Also, B. alicastrum and P. piscipula were the most preferred plants with intakes of 9.04 and 7.72 g DM/kg live weight (LW), respectively (P<0.05). In the absence of B. alicastrum (Experiment 2), the sheep changed their selectivity by increasing their intake of P. piscipula (8.73 g DM/kg LW) and L. latisiliquum (7.51 g DM/kg LW), but not A. pennatula (3.30 g DM/kg LW) (P<0.05). Neutral detergent fibre (NDF) was associated with IVDMD and IVGP (P<0.05). In Experiment 1, NDF was a better predictor of intake than polyphenolic compounds (P<0.05), but not in Experiment 2. It was concluded that tannins (at levels typically present in tropical forage trees) do not affect the intake of tanniniferous plants by sheep with browsing experience. These results widen the potential uses of these plants in sustainable grazing system for small ruminants. Further studies are needed to explore trade-off when using tanniniferous plants as nutraceuticals.